Rectifiers are generally employed to convert AC voltage to DC voltage. For example, rectifiers may be used in conjunction with AC generators to convert and condition power so that it can be stored in a battery. One specific type of rectifier is a rotating rectifier assembly. Rotating rectifier assemblies are used in brushless wound field synchronous generators.
Brushless wound field synchronous generators include a main machine and a brushless excitation system. The main machine produces the output power of the generator and includes a main armature (stator) and a main field (rotor). The main armature includes a three phase winding. The main field includes a DC field winding which requires excitation voltage to create an electromagnet such that there are north-south pole pairs on the rotor. The main field rotates on the shaft, such that when DC voltage is sourced to it, an AC voltage is induced in the three phase winding included on the main armature. The induced AC voltage in the three phase winding is utilized for output power.
The brushless excitation system includes an exciter field (stator) and an exciter armature (rotor) and a rotating rectifier. The exciter field, similar to the main field, includes a winding that uses voltage to create an electromagnet. The exciter armature, similar to the main armature, includes a three phase AC winding. The exciter armature rotates on the shaft, such that when the exciter field is excited with DC voltage, an AC voltage is induced in the exciter armature. The rotating rectifier converts the AC voltage from the exciter armature to DC voltage. The DC voltage output from the rotating rectifier is applied to the main field. Such rectifiers are designed to rotate on the shaft with the exciter armature and the main field.
Rectifiers include a combination of diodes and a snubber circuit, which are electrically connected via bus bars and between an AC bus and a DC bus, so as to form a suitable rectifier circuit. The snubber circuit can include any series or parallel combination of resistors, capacitors and/or inductors to condition the voltage and current waveforms of the rectifier. The diodes, snubber circuit, and bus bars are typically embedded in recesses formed in an annular insulator ring. The insulator ring serves to electrically insulate the components, while providing structural support so as to maintain the position thereof. The bus bars, resistors, diodes, etc. are then fastened into place on the insulator ring. For example, the bus bars are fastened by screws on either end, with the screws also each fastening to a conductive spring. The springs, in turn, hold the diodes and resistors in place, while providing electrical connection with the bus bar. Each screw is threaded in from the inside diameter of the insulator ring outwards (i.e., “side inserted”) into tapped holes formed in the insulator ring.